A three-dimensional unstructured incompressible RANS code has been developed using artificial compressibility and Spalart-Allmaras eddy viscosity model. A node-based finite volume method is used in which all flow variables are defined at the vertices of tetrahedrons in an unstructured grid. The inviscid fluxes are computed by using the Roe's flux difference splitting method, and higher order accuracy is attained by data reconstruction based on Taylor series expansion. Gauss theorem is used to formulate necessary gradients. For time integration, an implicit scheme based on linearized Euler backward method is used. A tetrahedral unstructured grid generation code has been also developed and applied to the tip clearance flow in a highly staggered cascade. Surface grids are first generated in the flow passage and blade tip by using several triangulation methods including Delaunay triangulation, advancing front method and advancing layer method. Then the whole computational domain including tip gap region is filled with prisms using the surface grids. Each prism is divided into three tetrahedrons. To accomplish this division in a consistent manner, connectivity pattern is assigned to each triangle in the surface grids. A new algorithm is devised to assign the connectivity pattern without reference to the particular method of triangulation. This technique offers great flexibility in surface grid generation. The code has been validated by comparisons with available computational and experimental results for several test cases: invisicd flow around NACA section, laminar and turbulent flow over a flat plate, turbulent flow through double-circular arc cascade and laminar flow through a square duct with 90° bend. For the laminar flat plate case, the velocity profile and skin friction coefficient are in excellent agreement with Blasius solution. For the turbulent flat plate case, velocity profiles are in full agreement with the law of the wall up to Reynolds number of 1.0E8, however, the skin friction coefficient is under-predicted by about 10% in comparison with empirical formula. Blade loading for the two-dimensional circular arc cascade is also compared with experiments. The results obtained with the experimental inflow angle (51.5° ) show some discrepancies at the trailing edge and severely under-predict the suction peak at the leading edge. These discrepancies are completely remedied if the inflow angle is increased to 53.5° . The code is also capable of predicting the secondary flow in the square duct with 90° bend, and the velocity profiles are in good agreement with measurements and published Navier-Stokes computations. Finally the code is applied to a linear cascade that has GE rotor B section with tip clearance and a high stagger angle of 56.9° . The overall structure of the tip clearance flow is well predicted. Loss of loading due to tip leakage flow and reloading due to tip leakage vortex are presented. On the end wall, separation line of the tip leakage vortex and reattachment line of passage vortex are identified. The location of the tip leakage vortex in the passage agrees very well with oil flow visualization. Separation bubble on the blade tip is also predicted. Mean streamwise velocity contours and cross sectional velocity vectors are compared with experimental results in the near wake, and good agreements are observed. It is concluded that Spalart-Allmaras turbulence model is adequate for this type of flow field except at locations where the tip leakage vortex of one blade interacts with the wake of a following blade. This situation may prevail for blades with longer span and/or in the far wake. Prediction of such an interaction presents a challenge to RANS computations. The effects of blade span on the flow structure have been also investigated. Two cascades with blades of aspect ratios of 0.5 and 1.0 are considered. By comparing pressure distributions on the blade, it is shown that the aspect ratio has strong effects on loading distribution on the blade although the tip gap height is very small (0.016 chord). Grid convergence study has been carried out with three different grids for pressure distributions and limiting streamlines on the end wall. / Ph. D.

The blood-brain barrier (BBB) is regulated by factors that can be secreted by multiple cell types, including astrocytes, that maintain the BBB in health and promote repair after injury. However, astrocyte contributions to the BBB are largely assumed from transplantation studies in which astrocyte progenitor grafts conferred BBB-like properties to tissues that normally lack a BBB. To determine if astrocytes contribute an essential and non-redundant function in maintaining the healthy BBB, I genetically ablated a small number of astrocytes using a conditional, tamoxifen-inducible mouse model. Within 2 hours after induction, I observed sparse astrocyte death in the cortex and leakage of the small molecule Cadaverine and large plasma protein fibrinogen, which are normally contained by a functional BBB. Vessels within regions of ablated astrocytes showed reduced expression of the tight junction protein zonula occludens-1, indicating impairment of the physical barrier formed between endothelial cells. Cadaverine leakage persisted for weeks, a feature I also found in mice after mild concussive traumatic brain injury (cTBI), thus highlighting the potential for revealing astrocyte roles in post-injury repair. Unlike the genetic ablation model, astrocytes within Cadaverine leakage areas did not undergo cell death after cTBI and instead downregulated homeostatic proteins. Our preliminary results show this atypical phenotype appearing 10 minutes after cTBI, along with severe vessel rupture, BBB leakage, and disruption of endfoot and basement membrane proteins. This damage persists for months, suggesting that the BBB fails to repair in these areas. Our results provide direct in-vivo evidence for essential astrocyte roles in the maintenance of the healthy BBB. Maintenance and/or repair fail after mild concussive cTBI, possibly contributing to irreversible progression to neurodegenerative diseases. / Doctor of Philosophy / The blood-brain barrier (BBB) is a unique property of blood vessels in the Central Nervous System (CNS) different from other vessels in the body. The physically tight barrier of the BBB is formed by tight junction proteins between endothelial cells and limits paracellular diffusion. The metabolic barrier is formed by concentrations of glucose transporters that promote transport of essential nutrients to the brain. Lastly, a transport barrier limits the passage of molecules and cells across the endothelial cell layer, preventing the entry of non-essential molecules, including pathogens and immune cells found in the blood. The BBB is thought to be induced and maintained by factors secreted by nearby cells in the brain. Among these cells are astrocytes, a type of glial cell that nearly completely cover blood vessels with their processes called endfeet. This strategic positioning led the field to assume that astrocytes are responsible for generating the unique properties of the BBB. Yet little direct evidence exists to support this conclusion, and newer evidence calls into question if astrocytes are even needed for BBB functions. To test this, I used a genetic mouse model to induce death of small numbers of astrocytes in adult mice. This caused leakage of blood contents of various sizes into the brain. In addition, the tight junction proteins responsible for forming the physical BBB were disrupted. These effects remained for weeks, a feature I also found after mild concussive traumatic brain injury (cTBI). This suggests that astrocytes may have an additional function in repairing the injured BBB. Our results demonstrate an essential role for astrocytes in the maintenance of the healthy adult BBB. Maintenance and/or its repair fail after cTBI, possibly contributing to the cascade into irreversible progression to neurodegenerative diseases.

Mild traumatic brain injury (mTBI)/ concussion accounts for 70-90% of all reported TBI cases in the United States and can cause long-term neurological outcomes that negatively impact quality of life. Previous studies revealed that increased blood-brain barrier (BBB) leakage is correlated with poor neurological outcomes after mTBI, yet the biological mechanisms linking BBB damage to the onset of neurological deficits after mTBI are not well understood. Previously, we found that astrocytes lose expression of homeostatic proteins after mTBI, characterizing the changes in astrocytic protein expression as an "atypical astrocyte response." Yet, the upstream mechanisms that induce this atypical astrocyte response after mTBI have yet to be elucidated. In models of more severe TBI, exposure to blood-borne factors triggers astrogliosis via upregulation in markers, such as glial fibrillary acidic protein (GFAP), but how exposure to blood-borne factors affects astrocyte protein expression in the context of mTBI is not well understood. Therefore, we hypothesized that mTBI-induced BBB damage causes atypical astrocytes via exposure to blood-borne factors. To test this hypothesis, we use a mTBI mouse model, two-photon microscopy, an endothelial cell-specific genetic ablation model, and serum-free primary astrocyte cultures. Here, we found that mTBI causes BBB damage through the loss of proteins involved in maintaining the BBB's physical and metabolic barriers, and BBB damage is sustained long-term after injury. Also, we demonstrated that leakage of blood-borne factors is sufficient to trigger atypical astrocytes, and plasma exposure triggers a similar response in vitro. Overall, these findings suggest that mTBI induces long-term BBB damage, and exposure to blood-borne factors triggers the loss of key homeostatic astrocytic proteins involved in maintaining healthy neuronal function. / Doctor of Philosophy / Mild traumatic brain injury (mTBI)/ concussion makes up 70-90% of all TBI cases reported in the United States and is commonly observed after car crashes, sports-related tackles, and blast exposure during military combat. People who experience mTBI develop debilitating long-term neurological consequences, such as sleep disturbances, depression, and dementia. Clinical data suggests mTBI causes damage to the barrier between the brain and blood, known as the blood-brain barrier (BBB). This damage has been correlated to the onset of poor neurological deficits, yet how damage to this barrier is causally linked to long-term neurological consequences remains to be fully understood. In our lab, we found that mTBI causes loss of proteins important for maintaining a healthy environment in the brain in specialized cells called astrocytes. However, the biological events that trigger the loss of protein expression in astrocytes after mTBI have yet to be fully investigated. Thus, we hypothesized that mTBI causes loss of these proteins via leakage of blood-borne factors. To test this hypothesis, we used a mTBI mouse model, two-photon microscopy, genetic manipulation, and cell cultures. In our studies, we found that mTBI triggers BBB damage via loss of proteins that make up its protective properties. Also, we demonstrated that leakage of blood-borne factors is sufficient to cause loss of astrocyte-specific proteins both in brain and cell cultures. Altogether, we show that a single mTBI is sufficient to cause loss of astrocyte-specific protein expression via exposure to blood-borne factors. These findings may point to targeting either the blood-borne factor(s) or their corresponding receptor pathways in astrocytes to halt the progression of long-term neurological deficits after mTBI.

Side-Channel Analysis (SCA) is an implementation attack where an adversary exploits unintentional outputs of a cryptographic module to reveal secret information. Unintentional outputs, also called side-channel outputs, include power consumption, electromagnetic radiation, execution time, photonic emissions, acoustic waves and many more. The real threat of SCA lies in the ability to mount attacks over small parts of the key and to aggregate information over many different traces. The cryptographic community acknowledges that SCA can break any security module if the adequate protection is not implemented. In this dissertation, we propose several advances in side-channel attacks and countermeasures. We focus on symmetric cryptographic primitives, namely: block-ciphers and hashing functions. In the first part, we focus on improving side-channel attacks. First, we propose a new method to profile highly parallel cryptographic modules. Profiling, in the context of SCA, characterizes the power consumption of a fully-controlled module to extract power signatures. Then, the power signatures are used to attack a similar module. Parallel designs show excessive algorithmic-noise in the power trace. Hence, we propose a novel attack that takes design parallelism into consideration, which results in a more powerful attack. Also, we propose the first comprehensive SCA of the new secure hashing function mbox{SHA-3}. Although the main application of mbox{SHA-3} is hashing, there are other keyed applications including Message Authentication Codes (MACs), where protection against SCA is required. We study the SCA properties of all the operations involved in mbox{SHA-3}. We also study the effect of changing the key-length on the difficulty of mounting attacks. Indeed, changing the key-length changes the attack methodology. Hence, we propose complete attacks against five different case studies, and propose a systematic algorithm to choose an attack methodology based on the key-length. In the second part, we propose different techniques for protection against SCA. Indeed, the threat of SCA can be mitigated if the secret key changes before every execution. Although many contributions, in the domain of leakage resilient cryptography, tried to achieve this goal, the proposed solutions were inefficient and required very high implementation cost. Hence, we highlight a generic framework for efficient leakage resiliency through lightweight key-updating. Then, we propose two complete solutions for protecting AES modes of operation. One uses a dedicated circuit for key-updating, while the other uses the underlying AES block cipher itself. The first one requires small area (for the additional circuit) but achieves negligible performance overhead. The second one has no area overhead but requires small performance overhead. Also, we address the problem of executing all the applications of hashing functions, e.g. the unkeyed application of regular hashing and the keyed application of generating MACs, on the same core. We observe that, running unkeyed application on an SCA-protected core will involve a huge loss of performance (3x to 4x). Hence, we propose a novel SCA-protected core for hashing. Our core has no overhead in unkeyed applications, and negligible overhead in keyed ones. Our research provides a better understanding of side-channel analysis and supports the cryptographic community with lightweight and efficient countermeasures. / Ph. D.

To prevent melting of turbine blades, numerous cooling schemes have been developed to cool the blades using cooler air from the compressor. Unfortunately, the clearance gap between adjacent hub sections allows coolant to leak into the hub region. Coolant flow also leaks into the hub region through gaps between individual stages. The results of a combined experimental and computational study of cooling along the hub of a first stage turbine blade caused by leakage flows are discussed in detail. Additionally, this study examines a novel cooling feature, called a microcircuit, which combines internal convective cooling with external film cooling. For the experimental investigation, scaled up blades were tested in a low speed wind tunnel. Adiabatic effectiveness measurements were made with infrared thermography of the entire hub region for a range of leakage flow conditions. For the computations, a commercially available computational fluid dynamics (CFD) code, FLUENT 6.0, was used to simulate the various flows. Results show that featherseal leakage flows provide small cooling benefits to the hub. Increases in featherseal flow provide no additional cooling to the hub region. Unlike the featherseal, leakage flows from the front rim provide ample cooling to the hub region, especially the leading edge of the blade passage. None of the leakage flows provide significant cooling to the pressure side region of the hub or trailing edge suction side. With the addition of the hub microcircuits, there is improved hub cooling of the suction side of the blades. Though the coolant exit uniformity was low and affected by the featherseal flow, the microcircuits were shown to provide more cooling along the hub region. Good agreements were observed between the computational and experimental results, though computations over-predicted front rim cooling and microcircuit uniformity. / Master of Science

This thesis investigates the application of an iterative leakage-based precoding algorithm to practical multiuser-MIMO systems. We consider the effect of practical impairments including imperfect channel state information, transmit antenna correlation, and time-varying channels. Solutions are derived which improve performance of the algorithm with imperfect channel state information at the transmitter by leveraging knowledge of the second-order statistics of the error. From this work we draw a number of conclusions on how imperfect channel state information may impact the system design including the importance of interference suppression at the receiver and the selection of the number of co-scheduled users. We also demonstrate an efficient approach to improve the convergence of the algorithm when using interference-rejection-combining receivers. Finally, we conduct simulations of an LTE-A system employing the improved algorithm to show its utility for modern communication systems. / Master of Science

Over the recent years many people have been trying to reduce the size and weight of magnetic components and thus the overall system [ 19 ]. One attempt at this is to increase the switching frequency of the system. However, this attempt has its limitations due to increased device switching losses. Device limitations usually confine this frequency to lower value than is desired. An effective approach, reducing the size and weight is to use the planar magnetics for possible integration with the power circuit and thus eliminating the associated interconnections. Planar magnetics uses the printed circuit board as the windings. This will allow the magnetic component to be implemented into the circuit. The integration of the magnetic components and power circuit will decrease the number of connections, reduce the height, and ensure the parasitic repeatability. Having external connections can cause problems in the system. In this case the system must carry a large amount of current. The connections can cause heating from resistance and inductance of the connection. The planar approach also will decrease the height of the system. This is because the planar magnetic cores have a higher surface area with a decreased height. This can reduce the height of the system by 25 %- 50 % [ 19 ]. The parasitic repeatability is also a very important factor. In many cases the typology relies on the parasitic elements for energy storage. Since, the parasitic elements are mainly a result from the geometry of the system; and the planar system has the windings made from the printed circuit board, the parasitic elements will be very consistent through the manufacturing process. For topologies that rely on the parasitic elements for soft switching, the planar design can incorporate parasitic elements with the leakage components for the soft-switching requirement. This thesis redefines the conventional term of leakage inductance as the sum of a set of lumped parasitic inductances and the transformer leakage inductance for the integrated planar magnetics and inverter power circuitry. For the conventional non-integrated transformer, either planar or non-planar, the leakage inductance is defined between two terminals of the transformer. However, for the integrated planar magnetics, the new lumped parasitic and leakage inductance should include the inverter switch and dc bus interconnections. The transformer was first designed using a closed-form solution for a known geometry with different copper thickness. The calculated leakage inductance was then verified with finite element analysis and the impedance analyzer measurement. It was found that the theoretical calculation and the finite element analysis results agreed very well, but the measurement was more than one order of magnitude higher. This prompted the study of interconnect parasitics. With geometrical structure and proper termination and lumping, a set of parasitic inductances were defined, and the results were verified with measurements of both impedance analyzer and phase-shifted modulated full-bridge inverter testing. In addition to parasitic inductance analysis, the flux distribution and associated thermal performance of the planar structure were also studied with finite element analysis. The resulting plots of flux distribution and temperature profile indicate the key locations of mechanical mounting and heat sinking. Overall the thesis covers essential design considerations in electrical, mechanical, and thermal aspects for the planar magnetics integration. / Master of Science

The use of computers in the modern world has become prevalent in all aspects of life. The size of these machines has decreased dramatically while the capability has increased exponentially. A special DC-DC converter called a VRM (Voltage Regulator Module) is used to power these machines. The VRM faces the task of supplying high current and high di/dt to the microprocessor while maintaining a tight load regulation. As computers have advanced, so have the VRM's used to power them. Increasing the current and di/dt of the VRM to keep up with the increasing demands of the microprocessor does not come without a cost. To provide the increased di/dt, the VRM must use a higher number of capacitors to supply the transient energy. This is an undesirable solution because of the increased cost and real estate demands this would lead to in the future. Another solution to this problem is to increase the switching frequency and control bandwidth of the VRM. As the switching frequency increases the VRM is faced with efficiency and thermal problems. The current buck topologies suffer large drops in efficiency as the frequency increases from high switching losses. Resonant or soft switching topologies can provide a relief from the high switching loss for high frequency power conversion. One disadvantage of the resonant schemes is the increased conduction losses produced by the circulating energy required to produce soft switching. As the frequency rises, the additional conduction loss in the resonant schemes can be smaller than the switching loss encountered in the hard switched buck. The topology studied in this work is the 12V non-isolated ZVS self-driven presented in [1]. This scheme offered an increased efficiency over the state of the art industry design and also increased the switching frequency for capacitor reduction. The goal of this research was to study this topology and improve the magnetic design to decrease the cost while maintaining the superior performance. The magnetics used in resonant converters are very important to the success of the design. Often, the leakage inductance of the magnetics is used to control the ZVS or ZCS switching operation. This work presents a new improved magnetic solution for use in the 12V non-isolated ZVS self-driven scheme which increases circuit operation, flexibility, and production feasibility. The improved magnetic structure is simulated using 3D FEA verification and verified in hardware design. / Master of Science

Yes / This paper describes the design, development, deployment and performance assessment of a prototype system for monitoring the 'health' of a water distribution network based on the temperature distribution and time-dependent variations in temperature across the network. It has been found that the water temperature can reveal unusual events in a water distribution network, indicated by dynamic variations in spatial temperature differential. Based on this indication it is shown how patterns of changes in the water temperature can be analysed using AQUIS pipeline distribution software and used in conjunction with hydraulic (e.g. flow and pressure) sensors to indicate the state of ¿health¿ of the network during operation.

Yes / This paper describes an automated event detection and location system for water distribution pipelines which is based upon low-cost sensor technology and signature analysis by an Artificial Neural Network (ANN). The development of a low cost failure sensor which measures the opacity or cloudiness of the local water flow has been designed, developed and validated, and an ANN based system is then described which uses time series data produced by sensors to construct an empirical model for time series prediction and classification of events. These two components have been installed, tested and verified in an experimental site in a UK water distribution system. Verification of the system has been achieved from a series of simulated burst trials which have provided real data sets. It is concluded that the system has potential in water distribution network management.